Scientists have discovered that fat cells in the knee secrete a protein linked to arthritis, a finding that paves the way for new gene therapies that could offer relief and mobility to millions worldwide. “We found that fat in the knee joints secretes a protein called pro-factor D which gives rise to another protein known as factor D that is linked to arthritis,” said Nirmal Banda, Ph.D., associate professor of medicine in the Division of Rheumatology at the University of Colorado School of Medicine. “Without factor D, mice cannot get rheumatoid arthritis.”